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If the query were repeated in the same
transaction, it would return a different set of results, so any changes made on the
basis of the original results may no longer be valid. Data that was read once can
return different results if the data is read again later in the same transaction.
190 | Chapter 8: Oracle Multiuser Concurrency
Phantom reads
Also occur as a result of changes made by another transaction. One transaction
makes a query based on a particular condition. After the data has been returned
to the first transaction, but before the first transaction is complete, another
transaction inserts into the database new rows that meet the selection criteria for
the first transaction. If the first SQL statement in a transaction returned the
number of rows that initially satisfied the selection criteria, and then performed
an action on the rows that satisfied the selection criteria later in the transaction,
the number of rows affected would be different from the initial number of rows
indicated, based on the inclusion of new phantom rows.


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